Laser-Induced Graphitization Interior to Bulk Diamond Forming Monolithic Electronic Structures

Diamond is a transparent ultra-wide bandgap insulator which has many unique properties (e.g., high dielectric strength, exceptional thermal conductivity, chemical inertness, etc.). As a metastable allotrope of carbon, diamond’s sp3-hybridized lattice can be transformed into sp2-hybridized graphite through the selective application of localized heating. Since diamond is transparent in a wide wavelength range (from ultraviolet to radio waves), laser radiation can be focused not only on the crystal surface but also at any point in its bulk. The techniques of laser microstructuring of diamond crystals make it possible to form graphitized microstructures of different shapes in their bulk. The influence of the processing parameters on the internal structure and conductivity of laser-modified material in diamond bulk is analyzed.<br/><br/>Two laser wavelengths, two optical configurations, and variable energy densities were precisely applied to single crystal substrates of CVD and HPT origins and varied purity levels. The nature of the graphitization as dependent on Gaussian beam and Bessel beam application was examined visually and electrically. The localization of laser graphitization associated with the Gaussian beam and the continuum nature of conversion of the Bessel beam is reported. Dimensionally equivalent ‘wires’ and ‘plates’ of graphitic regions were created in the interior of the diamond achieving relevant electronic structures. For example, parallel plates of conductive graphitized regions sub-micron thick and &gt; 1,000 microns square, with varying spacing and area, were created. Parallel plates with spacings as small as 1 micron were formed. These parallel plates were laser formed vertically and horizontally to the largest diamond surface resulting in capacitors which were evaluated electrically and the capacitive values are reported.<br/><br/>The aforementioned properties of diamond, particularly in single crystal, are of keen interest given the anticipated high breakdown voltage of diamond. The methods and materials described extrapolate to capacitors of unparalleled energy density.